A. Field of the Invention
The present invention relates to a soldering flux suitable for soldering electronic components and to a composition that contains this soldering flux.
B. Description of the Related Art
Many soldering fluxes are obtained by adding an activator consisting of an organic acid, a halide salt or a halogen compound to a rosin or a rosin-modified resin. However, these soldering fluxes remain as residues on printed circuit boards following completion of a soldering operation, and these residues are often the cause of substrate corrosion, migration, and so on. In addition, in cases where printed circuit boards on which residues remain are sealed with a resin (a silicone gel, epoxy resin, and so on), flux residues remaining following completion of a soldering operation can inhibit curing of the sealing resin, and this can affect adhesion to a substrate and insulating properties. Therefore, cleaning with a freon substitute or an organic solvent is carried out upon completion of a soldering operation in order to remove these residues. However, restrictions on cleaning agents are currently in place due to environmental problems caused by freons and VOCs.
Epoxy resin-containing fluxes are known as a type of flux which do not cause corrosion or migration and which do not inhibit curing of a sealing resin even if flux residues are not removed by cleaning (see Japanese Patent Application Publication No. 2000-216300). In general, epoxy-based fluxes are constituted from an epoxy resin as the main component, an organic acid or amine that is a curing agent or activator, and an alcoholic solvent. In cases where a cream solder that contains an epoxy-based flux is used to mount a component on a printed circuit board, the process is designed so that a curing reaction between the epoxy resin and a carboxylic acid occurs when removing an oxide film on the surface of a semiconductor by means of a carboxylic acid during reflow soldering, and the curing reaction is terminated when the solder melts and the soldering is complete. Following the soldering, a cured product of the epoxy resin remains as a flux residue. Compared to residues of commonly used rosin-based fluxes, this epoxy resin is superior in terms of not impairing adhesion between a printed circuit board and a sealing resin and exhibiting excellent insulating properties when sealing with a resin without cleaning following soldering.
Furthermore, a flux is known whereby even in cases where soldering is carried out using a lead-free solder having a melting point of 190 to 240° C., the activating properties of the flux are maintained, solder wettability is good and curing of a sealing resin is not impaired even if flux residues are not cleaned (see Japanese Patent Application Publication No. 2002-239785).
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.